Pulse echo altimeter with mechanically driven indicator



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PULSE ECHO ALTIMETER WITH MEcHANIcALLY DRIVEN INDICATOR Filed July 22,1948 4 Sheets-Sheet l July 4, 195@ woLFF ETAL PULSE EcHo ALTIMET-R wlwMECHANICALLY DRIVEN INDICATOR Filed July 22, 1948 WM5. Wwf

l l l l I l I i l. woLr-'F ETAL PULSE EcHo ALTIMETER wrm MECHANICALLYDRIVEN INDICATOR July 4, 1950 Filed July 22, 1948 aw .mf/raam 314, i950a. woLFF Erm. 2,513,983

PULSE EcHo Mmmm wrmr mcHANIcAwz DRIVEN INDIcAToR 4 Sheets-Sheet 4 FiledJuly 22, 1948 Patented July 4, 1956 PULSE ECHO AVLTIMETER WITH MECHANI-CALLY DRIVEN INDICATOR Application July 22,1948, Serial No. 40,146

12 claims. i

Our invention relates to radio distance measuring systems andparticularly to systems of the pulse-echo type that provide a directreading as by means of a pointer and dial.

An object of the invention is to provide an improved pulseecho distancemeasuring system of the direct reading type.

A further object of the invention is to provide a pulse-echo distancemeasuring system of improved accuracy.

A still further object of the invention is to provide an improvedpulse-echo radio altimeter of the type wherein the altitude is shown bya dial and pointer or similar indicating means.

A still further object of the invention is to provide a pulse-echodistance measuring system wherein a mechanical type distance indicatingdevice provides an'indication having an accuracy determined by pulsecoincidence.

A still further object of the invention is to provide an improved methodof and means for obtaining a distance reading in a pulse-echo distancemeasuring system.

According to the present invention there is a coarse control and a necontrol in a system of the type that includes a servo or follow-up motorfor driving the system to and for holding it at a balance point. Themotor in the example to be described drives the contact arm of abalancing potentiometer to which is coupled the pointer of thedistance-indicating dial. In order to obtain the fine control the motoralso drives a goniometer-type phase shifter through a plurality ofrotation for each rotation of the potentiometer arm. The goniometerphase shifter is tied into the system so as to produce a repetitivevoltage as the goniometer is rotated. This repetitive voltage is afunction of the angular position of the goniometer rotor and of-thepropagation time of a transmitted pulse in travelling to the reflectingobject or target.

In effect, the voltage from the balancing po-v tentiometer is balancedagainst a comparison voltage that is a function of the propagation timeto the target thus providing the coarse control, and is also balancedagainst the repetitive voltage thus providing the iine control.Circuitwise, in the example described, the sum of the potentiometervoltage and the repetitive voltage is balanced against the comparisonvoltage that is a function of the propagation time to the target.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which:

Figure 1 is a circuit and block diagram of one embodiment of theinvention,

Figure 2 is a circuit diagram of a start-stop circuit that may beemployed in the system ot rFigure 1,

Figures 2a and 2b are groups of graphs that are referred to inexplaining the .operation of Figure 2,

Figure 2c is a'circuit diagram showing how a portion of Figure 2 may bemodified.

Figure 3-is a group of graphs that are referred to in explaining theoperation of the system of Figure 1, particularly with reference to the`startstop circuit associated with the goniometer,

Figure 5 is a graph showing the direct-current output of theother'start-stop circuit of Figure l,

Figure 6 is a graph showing the output of the potentiometer that isgeared to the goniometer in Figure 1, and l Figures 7 and 8 are graphsthat are referred to in explaining the operation of the system of Figure1.

In the several figures, similar parts and graphs are indicated bysimilar reference characters.

Figure 1 shows an embodiment of the invention comprising a, radio pulsetransmitter I0 and a pulse receiver II for receiving the transmittedpulses after reflection from an object or surface the distance of whichis to be determined. The duration and repetition period of thetransmitted radio pulses are determined by the usual considerations suchas the desired resolution, the desired range, etc., as is wellunderstood in the radar art.

The modulating pulses T are obtained' from a frequency divider I2 thatis supplied with a sine wave signal from an oscillator I3 whichpreferably is crystal controlled.

The portion of the system that would by itself y give a coarse distancereading will now be described. It comprises a start-stop circuitindicated by the blocks I4, I6 and I1. The modulating pulses T areapplied to the start portion I4 and the received pulses PR are appliedto the stop portion I 6. A circuit of this type will be describedhereinafter in connection with Figure 2. The output of the sawtooth andrectifier block I1 is a direct current or D.C. voltage E of negati-vepolarity having an amplitude that is a function of the distance out `tothe target or reecting object as will be explained hereinafter. Thisvoltage E, which is represented by the graph in Fig. 5, will be referredto as the comparison voltage.

` In order to obtain a dial reading of the target distance, the D.C.output of block I1 is applied 3 i through. a high impedance, such 'as a2 megohm resistor I8, to the grid of a vacuum tube I9. The tube I9-,isfor operating a relay 2I to drive a servo or follow-up motor 22 in onedirection or the other. In the example shown. the relay 2| is of themarginal type but other types may be preferred. The' relay coil 24 is inthe plate circuit of tube I8 and pulls armatures'l24 and 2l to an upposition or releases themto a down" position. Thus a battery 21 drivesthe motor 22 in one direction or the other depending upon whether thevoltage on the grid of tube Il is above or below a certain value.

I The motor 22 is coupled through gears 2l and 2l to the rotatable armII of a follow-up potentiometer 32. It is also coupled through anladditional gear 33 to a goniometer-type phase shifter 34 for obtainingthe desired ne distance reading as explained hereinafter. The design ofthe phase shifter I4 maybe of any suitable conventional design butpreferably it is as described in application Serial No. 677,450, nowPatent N0. 2,442,097, issued May 25, 1948, led Juliev 18, 1946, in thename of Stuart W. Seeley and entitled Electrical Networks for'PhaseShifters. In the present example, the gearing 29, ll has a 10 to 1ratio. The'potentiometer arm 3| supplies a yitself would operate asfollows:

Whenr'efiected signals are received from a particular target, thelpotentiometer arm 3| is driven to a position on resistor 12 where theresistor voltage is equal to the voltage supplied from the block I1 sothat the sumvoltage is zero, since the two voltages are of oppositepolarity. Thus zero voltage is applied to the grid of tube I8 and theananas The comparatively high frequency pulses Po are produced bysupplying sine'wave signal from the oscillator Il through the goniometerphase 4shifter 34, and by supplying the resulting phaseshifted sine waveI5 to the pulse-forming circuit 4i. Thus the phase or timing of thepulses Po Is a function of the position of the rotor of the goniometer24. The pulse-forming circuit 42 may be of well known design comprisinga clipping circuit for clipping the wave 3l to obtain a square wave 4II.The wave 4I is differentiated to obtain the wave i0 which is clipped toobtain the ldesired pulses Pa.

The output of the start-stop block 41 is a direct current having anamplitude that is a function of the time or phase relation of thereceived pulses ,Pa and the pulses Pa; therefore, this output is afunction of the propagation time from-the transmitter tothe target andof the angular position of the goniometer rotor. I

The output from block 41 is applied with negative polarity through ahigh impedance, such as a 2 megohm resistor 5I, and through the lead Ilto the grid end of resistor I8.

From the foregoing description, it will be seen that the potentiometeroutput and the output from the start-stop circuit 44, 46, 41 are addedto obtain a sum output at the adding unit I1, 5I, and that this sumoutput and the output from the start-stop circuit I4. I6, I1 arecompared or subtracted at the comparator unit Il. It

. shouldbe understood that the invention is not relay armatures go to aneutral or mid-way position to stop the motor 2. This relay action isobtained by properly biasing the tube I8., as by a cathode circuitbattery 4I, and by properly adjusting the relay 2|.

The pointer 42 of a dial' 43 having a distance scale thereon is coupledtothe potentiometer arm Il so that it also is driven to a position thatis a function of target distance whereby the distance can be read offthe distance scale, also, for obtaining a more exact reading a pointer42'. of a dial 43' is coupled to the shaft of the goniometer Assume now,for example. that the target moves out to increase the distance. Thenthe output from block I1 increases, the relay 2i operates to make motor22 drive the potentiometer arm II in the direction indicated by thearrow to supply an increased potentiometer voltage to balance theincreased voltage from block I1.v

When the two voltages are again equal, the armatures of relay 2l againgo to the mid-way position and the motor 22 is stopped. The reverseaction takes place when the target moves in to decrease the distance.

According to the present invention, the system comprises additionalcircuit means in combination with the above-described portion of .thesystem whereby a fine or exact positioning of the limited to theparticular adding orcomparison circuit illustrated as other suitablecircuits are well known in the art.J

Before describing the system operation in more detail, reference will bemade to Fig. 2 showing the details of one form of suitable start-stopcircuit.

Fig. 2 shows a specic form of start-stop circuit that is described andclaimed in application Serial No. 728,861, med-February 15, 1947, in thename of Randall C. Ballard and entitled Indicator l Circuit for PulseAltimeter.

The start pulses are supplied through a blocking condenser 56 to thegrid 51 of a vacuum tube I8. In the start-stop circuit I4, I6, I1 thestart pulses are the transmitter modulating pulses. The stoppulses aresupplied through a blocking capacitor 59 to the grid 6I of a vacuum tube62.

In the start-stop circuit I4, Il, I1 the stop pulses are the receivedpulses.

The vacuumy tube I8, which acts as a cathode follower tube. has theoperating voltage applied directly to its anode Il and has theanode-cathode impedance of the tube B2 connected in its cathode circuit,the anode I4 of tube 62 being connected directly to the cathode i0 ofthe tube 5I and the cathode 81 of the tube l2 being connected to ground.

yOperating voltage is applied to the anode I4 of tube 62 through aresistor il of high impedance. The distributed capacity between thecathode Ol' and ground is indicated at II. The capacity Il www `potential.

may be of the order of iive or ten micromicrofai-ads and serves to 'holdthe cathode 66 at the potential above ground to which it is driven whena pulse appears on the grid 51.

The grid 51 of tube 58 h as a slightly positive bias potential appliedto it from potentiometer resistor 1| by way of a grid resistor 12. Thegrid @I of the tube 62 has a negative'bias applied to it from a biasresistor 13 by way of a grid resistor 14, this bias voltage beingsucient to bias the tube 62 to cut-off.

The operation by which pulses appear om the cathode 66 or junction pointT having a duration equal to the interval between the start pulse andthe stop pulse will be better understood by referring to Figs. 2a and2b. In Fig. 2a there is illustrated the condition where the timeinterval between a transmitted pulse and the received pulse iscomparatively short. As soon as the transmitter modulating pulse ofpositive polarity appears on the grid 51, the junction point T goespositive as indicated by the graph marked combined output, this beingthe result of the cathode following the grid potential due to thecathode follower action. As soon as the positive received pulse appearson the grid 6I of tube B2, the tube 62 becomes conducting and bring thepoint T baci; substantially to ground potential. Thus, a positive pulseappears at T having a duration equal to the time interval between thefront edges of the two applied pulses.

Referring to Fig. 2b, the same action takes place but in this instancethe time interval between transmitted and received pulses is greaterthan in the rst example. The function of the distributed capacity 69 isevident here as well as in Fig. 2a as it will be noted that the positivepulse oi the "combined output at T maintains its voltage level after thetermination of the transmitted pulse. Upon the reception of thereflected pulse, the resulting low impedance of the tube 52 brings thepoint T back substantially to ground As before, the width of thepositive pulse at point T is a measure of the time interval between thefront edges of the two applied pulses.

The pulses taken off the point T are applied through a lead 16 and aIblocking capacitor 11 to the control grid 18 of a pentode 19 whichfunctions as the discharge tube of a sawtooth wave producing circuit. Acapacitor 8| across which a sawtooth voltage is to be produced isconnected between ground and the anode of the pentode la. Positive D.C.voltage is applied to capacitor di through the plate resistor 80 of thepentode 1Q.

The pentode yl!! is biassed beyond cut-oir and the capacitor 8| chargesto full plus B potential between successive pulses taken from the pointl T. Each time a positive pulse from the point`T is applied to the grid18 of the discharge tube, the capacitor 8| partially discharges throughthe tube 19. The amount of this discharge depends upon the duration ofthe applied pulse. Therefore, the amplitude of the resulting sawtoothwave produced across capacitor 8| is a function of the duration of thepulse applied from point T. This is illustratedyby the graphs in Figs.2a and 2b.

Preferably, the amplitude of the pulse from the point T is suicient todrive the grid 18 of the pentode 19 positive so as to make it draw gridcurrent. This eiectively clips the pulse at the grid 18 so that anyvariations in the pulse amplitude above a certain voltage level,indicated as the effective level in Figs. 2a and 2b, will not affect thedischarge rateof the sawtooth capacitor 3l. The sawtooth voltage fromcapacitor 8i is ap- 6 plied through a capacitor 82 to the cathode of adiode 83. Resistors 84 and 86 are connected from the cathode and theanode, respectively, of the diode 83 to ground, and -a filter capacitor81 is connected across the resistor 86. This provides a direct currentoutput of negative polarity.

The start-stop circuit 44, d6, 41 may be the same as shown in Fig. 2although, as shown in Fig. 2c, it may be preferred to provide in therectifier output circuit a bias battery 88 in place of the potentiometerbias battery 3Ib shown in Fig. 1.

Figs. 3 and 4 illustrate more clearly the operation of the start-stopcircuit M, t6, d1 to which the received pulses and thegoniometer-controlled pulses are applied. Assuming that these pulses arebeing applied' to the start-stop circuit in nearly coincident phaserelation as indicated in Fig. 3 by the pulses Pa and Pc, then theresulting recurring sawtooth pulse M will have its maximum amplitude HIas shown when the pulse Po immediately follows the pulse Ra. When thepulse PG immediately precedes the pulse PR then the sawtooth pulse M hasminimum value. From minimum value to maximum value there is a very rapidchange in amplitude. The sawtooth wave M corresponds, of course, to thesawtooth waves shown in Figs. 2a and 2b.

Now assume the target moves out and assume that the goniometer settinghas not changed. Now the received'pulses P'a starts the sawtooth pulselater but it is still stopped at the same time by a pulse PG whereby thesawtooth height is now H2. Any motion of the goniometer to move theindicator to greater distances will increase the time between start andstop and have the same effect on the output of the start-stop circuit asreducing the target distance again would have. Thus the output of thiscircuit depends not only on the target position or the indicatorposition but on the extent to which they are brought into coincidence.

Now referring to Fig. 4, the graph G shows the direct current outputthat would be supplied from the start-stop circuit M, 66, G1 if thetarget were moving out and the goniometer were stationary, or if thetarget were stationary and indicator readings were decreasing or if bothwere happening simultaneously. It will be seen that the output ismaximum near pulse coincidence and decreases until the received pulse isnear coincidence with the next goniometer-controlled pulse. This samewave G is shown in Fig. 7 as the wave a plotted against ct d,-- 2

instead of against t as will be understood from the description ofoperation that follows. It will be seen that the wave is repetitive,there being one sawtooth for each goniometer-controlled pulse. Thereare, in the example shown, ten goniometercontrolled pulses PG for eachreceived pulse PR.

The complete operation of the system may be explained as follows:

(1) A pulse is radiated from the transmitter, and at a time t later thepulse reflected from the target at distance d returns to the receiver.The distance and time are related by the expression where c is thevelocity of transmission of radio waves.

.turnis emissies 7 (2) The servo-operated indicator is operatedbytherehirningpulse. Ifdiisthedistancoindicated on'the indicator. thenfor correct operation of the equipment.

(3) If di is not equal to a signal is applied to the servomotorftorotate the indicator to make et dig- 'rms is explained more muy below.(i) The signal applied to the servomotor control is made up of (a) thesignal generated by zo and- (b) two other signals which when added serveto remove ambiguity in the signal furnished by (a) These two signals areobtained by means of the potentiometer attached t'o the indicator and bymeans of the slow.sawtooth voltage started by the outgoing pulse andstopped by the received pulse. A

The way in which the signals add may best be shown in the following way:

vThe goniometer is geared to the indicator in such a way that thedistance indicated when it rotates through one complete rotation is 2fwhere f is the frequency applied to the goniometer from the crystalcontrolled oscillator Il.

Thus. it the lsystem is adjusted so that the center of the step in thefast sawtooth wave coincides with the received pulse when the indicatorregisered to introduce a time delay of The indicator is calibrated sothat the distance indicated (di) for N rotations is (seeabove). The timetaken for a radio wave to traveLto a target at this distance and rec 2ff which is exactly the time delay introduced by the in the locallygenerated pulse.

For intermediate distances the accuracy is affooted by the linearity ofthe goniometer phase- 8 rotation characteristic but is alwaysindependent again of this characteristic at the distancesInFig.7,grapha.isshownthcvoitagede v eloped by the fast sawtooth torotate the motor as a function of deviationV of the indicator fro itscorrect position. Since the indicator v correctly whenthismaybeplottcdintermsof l5 m order m have the indicator rotationcomet.

a voltage must be supplied for all to make di less and conversely forFig. 7, graph a. shows that the operation can be made correct for smalldeviations from but that there are a number of other positions at whichthe servo could lock spaced from the correct value.

'I'he voltages added by the slow sawtooth and the potentiometereliminate these incorrect locking points without aifecting the operationin the neighborhood of. the correct point materially.

Bince the slow sawtooth current output does not depend on the indicatorposition it is a functibn of t alone. Conversely since the potentiometeroutput depends only on the indicator position its output is a functionof d: alone. However the nature of the constant chosen for the operationof these circuits causes them in combination to be a function of Thisresults because the slopes as a function of d1 and t are chosen to makethe output of the two circuits equal-and opposite in sign when i. e. ifthe slow sawtooth circuit output is kit and the potentiometer output ishdi then EMTv The sum of the slow sawtooth output and the potentiometeroutput is plotted as a function of in Fig. '1, graph b. Although theratio of k: to k; is set by the conditions imposed, their magnitude isdisposable providing the ratio is maintained.Thevalueoflciischosentomaketheslopeof the slow sawtooth as a function oft the same in magnitude but opposite in sign to that of the fastsawtooth. Since the fast sawtooth and the 75 sum of -the slow sawtoothand the potentiometer` output are now all plotted variable they may-beadded directly to give the step c shown in Fig. 8. This represents theoutput applied to the motor control circuit in the equipment and givesthe following desirable features:

l. Output O for in terms of the same nel?.

2. Very rapid variation in voltage to return indicator to together,although in Fig. l and in the accompanying description it is indicatedthat the potentiometer output F and the fast sawtooth wave G (Fig. 4)are added. There is no error in referring to the addition in twodifferent ways because, as is well known, the order of addition of thewaves E, F and G is immaterial.

We claim as our invention:

l. A distance measuring system comprising means for transmitting pulsesof energy, means at substantially the same location as the transmittingmeans for receiving said pulses after reection from an object orsurface, means for producing a comparison voltage that has an amplitudethat is a function of the time interval between the transmission of apulse and reception of said pulse vafter reflection, a follow-up circuitcomprising means for producing-a follow-up voltage that also has anamplitude that is a function of said time interval and is at leastapproximately proportional to said comparison voltage,lmeans forproducing a series of accurately-spaced pulses means for synchronizingthe transmission of the transmitted pulses with selected ones of saidaccurately-spaced pulses, a distance indicator for indicating distancefrom said transmitting means to said reflecting object, a phase shifterfor shifting the phase of said control pulses through more than 360degrees. means including said follow-up circuit for operatingsaid-distance indicator and for causing said phase shifter to shift thephase of said control pulses as 'a function of said time interval, meansfor producing a repetitive voltage that has an amplitude that is afunction of the time interval between one of said control pulses and oneof said received pulses, means for addingr algebraically said follow-upvoltage, said repetitive voltage and said comparison voltage to obtain afollow-up control voltage that has the form of a step when plotted as afunction of where di is the distance indicated o'n said indicator, c isthe velocity of transmission of radio waves, and t is the time taken fora radio wave to travel from the transmitter to the reflecting object andback to the transmitter, and means for operating said follow-up circuitby said follow-up control voltage.

' age that also has an amplitude that is a function of said timeinterval and is at least approximately proportional to said comparisonvoltage, means for producing control pulses that have a repetition ratethat is a multiple of the repetition rate oi' said transmitted pulses,al distance indicator for indicating distance from said transmittingmeans to said reflecting object, a phase shifter for shifting the phaseof said control pulses through more than 360 degrees, means includingsaid follow-up circuit for operating said distance indicator and forcausing said phase shifter to shift the phase of said controlA pulses asa function of said time interval, means for producing a repetitivevoltage that has an amplitude that is a function of the time intervalbetween one of said control pulses and one of said received pulses,means for adding algebraically said follow-up voltage, said repetitivevoltage and said comparison voltage to obtain a follow-up controlvoltage that has the form of a step when plotted as a function of whered1 is the distance indicated on said indicator, c is the velocity oftransmission of radio waves, and t is the time taken for a radio wave totravel from the transmitter to the reflecting object and back to thetransmitter, and means for operating said follow-up circuit by saidfollow-up control voltage.

3. A pulse-echo distance measuring system comprising means fortransmitting pulses of energy and receiving them after reection from anobject, means for producing a first voltage having an amplitude that isa function of the time interval between transmission of a pulse andreception of said pulse after reflection, a main distance indicator thatindicates full range and a. phase shifter which is geared to saidindicator so that it is driven through 360 electrical degrees aplurality of times as said indicator is driven through its full range,means for producing a voltage Whose amplitude is a function of theangular position of the phase shifter and of said time interval, meanscomprising a follow-up circuit for driving said distance indicator, saidfollow-up circuit including means for developing a third voltage as afunction of the indicator position, and means for combining said threevoltages in said follow-up circuit to position said distance indicator.

4. The invention according` to claim 3 wherein 'a vernier distanceindicator is coupled to said phase shifter to be driven thereby.

5. A pulse-echo distance measuring system comprising means fortransmitting pulses of energy and receiving them after reflection froman object, means for producing a first voltage having an amplitude thatis a function of the time interval between transmission of a pulse andreception of said pulse after reflection, a distance indicator and agoniometer phase shifter which are geared together, means for producinga repetitive voltage as said phase shifter is rotated wtn the amplitudebining said three, voltages in said follow-up cir,

cuit to position said distance indicator.

6. A pulse-echo distance measuring system comprising means fortransmitting pulses of energy and receiving them after reflection froman object, an indicator for indicating the distance to saidobject, meansfor producing a first voltage which is a periodic function of saiddistance indicator reading and of the time interval between .j

transmission and reception of a pulse, said function having a form thatincludes a steep slope,

means for producing a second voltage which is a I function only lof saiddistance indication, means for producing a third voltage which is afunction only of said time interval, means for combining said threevoltages, and means for driving4 said distance indicator for maintainingsaid `combina-- tion at a predetermined value.

'1. A pulse-echo distance measuring system comprising means fortransmitting pulses of energy and receiving them after reflection froman object, an indicator for' indicating the distance to said object,means for producing a sawtooth Avoltage which is a periodic function ofsaid distance indicator reading and of the time interval between tionand reception of a. pulse,'said function having a form that includes asteep slope, means for, producing asecond voltage which is a functiononly of .said

distance indication, means for producing' a third voltage which is afunction only of said' time interval, means for combining said threevoltages, and means for driving said distance indicator for maintainingsaid combination at a predetermined value.

8. A pulse-echo distance indicator comprising .s means for'ftransmittingpulses of energy, means for receiving said pulses after renectionl froman object, means for producing a comparison voltage that is a functionofy the` time interval between transmission and reception of each of'said pulses, a mechanical type distance indicator, means'comprisingalfollow-up circuit for ldriving said indicator as a function of saidtime interval, said follow-up icircuit including means for producing afollow-up voltage and balanc- 9. A distance measuring system comprisingmeans for transmitting pulses oi' energy, means at substantially thesame location as the transmitting means for receivingsaid pulses afterreflection from an object or surface, means for producing a comparisonvoltage that has an amplitude that is a `function of the time intervalbetween the transmission of a pulse and reception of said pulse afterreflection, aV follow-up circuit comprisingmeans for producing'v afollowup voltage thatalso has an amplitude that is a function of saidtime' interval and is at least approximately proportional to saidcomparisonr voltage, means for producing control pulses that have arepetition rate that is a multiple of the repetition rate of saidtransmitted pulses, a distance indicator'for indicating distance fromsaid transmitting means to said reflecting object, a phase shifter forshifting the phase of said control pulses through more than 360 degrees,means includingv said follow-up circuit for operating said distanceindicator and f'or ,causing said phase shifter to shift the phase ofsaid control pulses as a function of said time interval, means 'forproducing a repetitive voltage that has an.

amplitude that is a function of the time interval between one of saidcontrol pulses and one of said received pulses, means for adding algelbraically said follow-up voltage and said repetitive voltage to obtaina` sum voltage, means for adding algebraically said sum. voltage of onepolarity with said comparison voltage of theopposite polarity to obtaina follow-up control voltage, and'rjmeans for operating said follow-upcircuit by said follow-up control voltage.

10. A distance measuring system comprising means for transmitting pulsesof energy, means for receiving said pulses after reection from an objector surface, means for obtaining a voltage that is a function of the timeinterval between the transmission of av pulse and its reception afterreflection, a distance indicator and a phase shifter that are gearedtogether, a follow-up system for driving said indicator as a function ofsaid time interval, said follow-up system includa ing means forproducing a follow-up voltage that is a function of said indicatorreading, means for obtaining an alternating-current voltage whose phaseor timing is a function of said indicator reading, and means for causingsaid followup system to drive said indicator to a position ing itagainst said comparison voltage, a phase shifter that may be driven toshift the phase 'of an applied signal by more than 360 degrees, meansfor applying to said phase shifter a signal having a repetition ratethat is a multiple of the repetitionlrate of said transmitted pulses,means for driving said phase shifter by' said follow-up circuit asafunction of said time interval and for causing it to shift thephase ofK said applied signal through 360 degrees times said multiple as saidfollow-up voltage goes from repetitive voltage thereto and balancing itagainst said comparison voltage.

'that is determined by the relative amplitudes of said three voltages asdetermined by the time a 4reflected pulse is received.

11. A pulse-echo system comprising a main distance indicator thatindicates full range and a phase shifter geared to said indicator sothat it is driven through 360 electrical degrees a plurality of times assaid indicator is driven through its full range, means for transmittingpulses of energy to a reflecting object and means for receiving saidpulses after reflection, means for producing a first voltage that variesas a function of the time interval between ltransmission and receptionof a reected pulse, means for producing a voltage that repeats each timesaid phase shifter is driven through 360 electrical degrees and thatvaries in phase or timing as a function of the position of the phaseshifter, and means for driving said indicator to a positien theft isdetermined by the amplitude of said first voltage that is reached duringsaid time interval and by the amplitude of said repetitive voltage thatis reached in the time interval between an instant determined by thephaseananas shifter position and the instant ofreception of a receivedpulse.

12. A pulse-echo system comprising a main distance indicator thatindicates full range and a phase shifter geared to said indicator sothat the phase shifter is driven through 360 elec'- trical degrees aplurality of times as said indicator is driven through its full range,means for transmitting pulses of energy to a reilecting object and meansforreceiving said pulses after reflection. means for producing a mstvoltage that varies as a function of the timeI interval betweentransmission and reception of a reilected pulse, means for producing avoltage that repeats each time said phase shifter is driven through 360electrical degrees and that varies in phase or timing as a function ofthe position of the phase shifter, means for obtaining a control voltagethat is a function of the time interval between a. point in the cycle ofsaid repetitive voltage and the reception of a reflected pulse, andmeans including a potentiometer 'means that produces a. follow-upvoltage that is a function of said indicator reading for driving saidindicator to a position that is determined by the1A amplitude of saidfirst voltage that is reached during said time interval and by theamplitude of said control voltage. y

' IRVING, WOLFF.

PHILIP J. HERBST.

REFERENCES man The following references are of record in the

